The present invention generally relates to a device for sensing acoustic signals and converting these signals to electrical signal outputs and vice versa. The invention more particularly relates to a listening device to sense acoustic signals underwater and to remain reliable and relatively unaffected by pressure and temperature changes encountered in an ocean's environment.
A variety of devices are currently used to sense underwater acoustic signals reliably under varying temperature and pressure conditions. Transduction mechanisms range from moving coil devices magnetostrictive and piezoelectric materials. The largest class of devices employs piezoelectric ceramic which has the disadvantages of being dense, fragile and expensive. A flexural disc device using a piezoelectric polymer film, polyvinylidene fluoride was developed by Powers and Sullivan at Naval Underwater Systems Center, New London, Connecticut. Polyvinylidene fluoride is a light, rugged and potentially inexpensive material. The above flexural disc device performs competitively with ceramic hydrophones for several applications. However, the flexural disc design often requires layers of piezoelectric polymer film to reach the desired sensitivity and capacitance and is particularly difficult to adapt to small diameter line arrays and spacial noise averaging.